JP3020765B2 - Surface coated tungsten carbide-alumina sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered body obtained by sintering a raw material powder, and more particularly, to a sintered body having high hardness, excellent toughness, and suitable for wear-resistant materials and tool materials. The present invention relates to a surface-coated tungsten carbide-alumina sintered body in which a surface coating layer is formed on a sintered body.

[0002]

2. Description of the Related Art Cemented carbides (WC-Co sintered bodies) have been applied to various industrial machine parts as materials having excellent wear resistance. However, when used as a cutting tool, there is a drawback that the wear resistance is poor.In recent years, the use of a cemented carbide alone as a cutting tool has been reduced. , Titanium carbide,
In many cases, titanium nitride or the like is used after being coated.

[0003] When a cemented carbide is used as a cutting tool, poor wear resistance is mainly caused by Co contained in the binder phase.
Is low. Under cutting conditions in recent years, the temperature of the tool edge easily reaches about 1200 ° C. during cutting. This temperature is close to the melting point of Co itself.
The C particles lose their bonding strength and become brittle and easily collapse.

Therefore, a sintered body using alumina (Al ₂ O ₃ ) instead of using Co as a binder phase forming component for WC has been proposed.

[0005]

However, since the WC-Al ₂ O ₃ sintered body has a poor sintering property, the WC-Al ₂ O ₃ sintered body is not compact unless a method of applying an external pressure such as a hot press method. Could not be converted. For this reason, there is a problem that this sintered body cannot be applied to large parts such as wear-resistant materials. For this reason, the conventional WC-A
At present, the l ₂ O ₃ sintered body can hardly be applied to cutting tools and the like.

[0006]

[Means for Solving the Problems] The present inventors have repeatedly studied the above problems and found that Al ₂ O
_{3 As} tungsten carbide dispersed in
By the presence of an appropriate amount of ₂ C, the sinterability is improved and a dense sintered body is obtained, and the toughness and hardness of the sintered body are improved. The present inventors have found that coating with an element or a compound of Al improves WC and W ₂ C inferior in oxidation resistance and improves wear resistance, leading to the present invention.

That is, the present invention comprises tungsten carbide and alumina as main components and has a W ₂ C (1
When the peak height of 01) surface is a peak height of the (100) plane of the I _1, WC and I _2, the peak intensity ratio represented by I ₁ / I ₂ is 1 / 1000-200 / 1000 A single-layer or multiple-layer surface coating layer is formed on the surface of the sintered body, and the surface coating layer is formed of a carbide, nitride, boride, carbonitride, carbonitride, A
It is composed of at least one compound selected from the group consisting of oxides and oxynitrides.

Hereinafter, the present invention will be described in detail. In the present invention, the tungsten carbide-alumina sintered body serving as a base material is composed of a phase composed of tungsten carbide and the remainder having a phase mainly composed of alumina. % By weight, in particular from 20 to 75% by weight. The reason why the ratio of the hard phase is limited to the above range is that if the tungsten carbide phase is less than 5% by weight, the effect of improving the strength and toughness of the sintered body tends to be small. This is because, even if a dense sintered body is obtained, the grain growth tends to be large and the strength tends to be low.

Further, according to the present invention, a significant feature is that the tungsten carbide component forming the hard phase comprises WC and W ₂ C. The amount of W ₂ C, in the X-ray diffraction measurement, of W ₂ C near 2θ = 39.6 ° (1
When the peak height of the (01) plane is I ₁ and the peak height of the (100) plane of WC near 2θ = 35.6 ° is I ₂ , I ₁
/ I ₂ is 1/1000 to ₂₀₀
/ 1000, especially 5/1000 to 50/1000. The reason for limiting the ratio to the above range is that if the ratio is smaller than 1/1000, the transverse rupture strength decreases, and if it exceeds 200/1000, the wear resistance decreases and application to cutting tools is difficult. is there.

[0010] Further, the crystal particle diameter of both tungsten carbide and alumina in the sintered body is desirably 10 µm or less, and if it exceeds 10 µm, the transverse rupture strength of the sintered body is reduced. It is particularly desirable that the cutting tool material has a thickness of 2 μm or less. However, this does not apply when using as a wear-resistant material other than a cutting tool.

Further, according to the present invention, the above WC-A
It is desirable to incorporate a sintering aid to improve the sintering property in l ₂ O ₃ quality material. As the sintering aid to be used, a substance known as a sintering aid for Al ₂ O ₃ is used. For example, in addition to MgO, CaO, SrO and SiO ₂ ,
Group 3a element oxides of the periodic table. These auxiliaries are contained in the sintered body in an amount of 0.02 to 8% by weight or less, particularly 0.5 to 5% by weight.
It is desirable to use it in a proportion of weight%. In addition, Yb, Nd, Er, Ce, S
m, Y, Gd, Dy and La.

In the present invention, the thickness of the sintered body is 0.3 to 30 μm by a chemical vapor deposition method, a physical vapor deposition method or the like.
m surface coating layers are formed. This surface coating layer is composed of a single layer or a multilayer of two or more layers.
It is composed of at least one compound selected from the group consisting of carbides, nitrides, carbonitrides, carbonitrides, and oxides and oxynitrides of Al. Elements of Group 4a of the periodic table include Ti, Zr, and Hf. The thickness of the surface coating layer is particularly preferably 1 to 12 μm.

In the production of the surface-coated tungsten carbide-alumina sintered body of the present invention, for example, the oxygen content is 0.05 to
W of 6.0% by weight and a carbon content of 5.0 to 6.3% by weight
After forming a mixed powder containing 5 to 95% by weight of C powder and the remainder mainly composed of alumina, it is fired in a non-oxidizing atmosphere at 1450 to 1950 ° C., and the peak height of the (101) plane of W ₂ C is set to I _1, when the WC of the peak height of the (100) plane was I _2, the peak intensity ratio represented by I ₁ / I ₂ is 1/100
W ₂ C is generated so as to be in the range of 0 to 200/1000.

That is, alumina powder, tungsten carbide powder and, if desired, a sintering aid are mixed in the above-mentioned ratio. At this time, the average particle size of the raw material powder to be blended is preferably 2 μm or less, particularly preferably 0.5 to 1.5 μm. When the average particle size is 2 μm or less, the grain growth during firing does not become excessive, and high bending strength is obtained. On the other hand, if the average particle size is larger than 2 μm, it is difficult to control the grain growth during firing, and both the strength and the toughness tend to decrease. On the other hand, if it is 0.5 μm or less, a sintered body excellent in characteristics can be obtained, but there is a problem that handling of powder becomes difficult in manufacturing.

The amount of W ₂ C in the sintered body can be controlled by the amount of oxygen and the amount of carbon in the tungsten carbide powder used. Specifically, the amount of oxygen in the tungsten carbide raw material powder is 0.05 to 6.0% by weight,
In addition, the carbon content needs to be 5.0 to 6.3% by weight. If the amount of oxygen is less than 0.05% by weight or the amount of carbon exceeds 6.3% by weight, the generation of W ₂ C becomes insufficient, and the bending strength decreases. When the amount of carbon is less than 5.0% by weight or the amount of oxygen exceeds 6.0% by weight, W ₂ C in the sintered body increases, the hardness of the sintered body decreases, and as a cutting tool, This is because the wear resistance when used is significantly reduced.

The mixture of each of the above-mentioned raw materials is formed into a desired shape by a desired forming means, for example, a die press, a cold isostatic press, an extrusion or the like, and then fired.

For firing, a normal firing method, a hot press method, a hot isostatic firing method, or the like is applied. According to the present invention,
By using the specific tungsten carbide raw material powder as described above, W ₂ C is generated in addition to WC. Firing is 14
It may be carried out at a temperature of 50 to 1950 ° C. in a reducing atmosphere in which an inert gas such as Ar or He or carbon or the like is present and in a pressurized or reduced pressure atmosphere for 0.5 to 6.0 hours. In order to obtain the consolidated, normal firing,
A sintered body having a relative density of 96% or more is prepared by a hot press method, and further subjected to hot isostatic sintering under a high pressure of 500 atm or more to achieve higher densification.

As described above, when the amount of oxygen in the WC increases, oxygen reacts with the carbon of the WC and is released as CO _{2 out} of the system due to the manufacturing method. ₂ C is generated, whereby the sinterability of the sintered body when used as, for example, a cutting tool is improved, and large-sized products and the like can be easily fired.

Then, a layer thickness of 0.3 to 30 μm is formed on the surface of the sintered body by a known chemical vapor deposition method, physical vapor deposition method or the like.
Is formed. This surface coating layer is composed of a single layer or a multilayer of two or more layers.
It is composed of at least one compound selected from the group consisting of carbides, nitrides, carbonitrides, carbonitrides, and oxides and oxynitrides of Al, such as N and Al ₂ O ₃ .

[0020]

According to the present invention, the presence of W ₂ C in addition to WC as tungsten carbide forming a hard phase increases the bonding strength between W ₂ C and Al ₂ O ₃ and WC,
The toughness and strength of the sintered body can be increased. Also,
WC and W ₂ C are poor in oxidation resistance and have a problem that when used as a cutting tool, they become fragile tungsten oxide during cutting.
Since a surface coating layer composed of at least one compound of oxides and oxynitrides of carbides, nitrides, carbonitrides, carbonitrides and Al of group a elements is formed, the oxidation resistance can be improved. Thereby, the wear resistance of the cutting tool can be improved. Therefore, a longer tool life can be expected in applications to cutting tools and the like. In addition, the present invention can be applied to various industrial parts requiring wear resistance other than cutting tools.

[0021]

EXAMPLE An Al ₂ O ₃ powder having an average particle size of 1 μm or less and a purity of 99.9% or more, and various tungsten carbide powders having an average particle size of 1.5 μm and having an oxygen content and a carbon content shown in Tables 1 and 2 were used. After weighing at the ratios shown in Tables 1 and 2, they were mixed and pulverized with a vibration mill for 12 hours. This powder was taken out, dried, and an organic binder was added to obtain a powder for press molding.

This material is filled in a mold, and 1000 kg /
press forming at a pressure of ² cm ² and then 350 kg / c
A pressure of m ² was applied and firing was performed at 1650 to 1950 ° C.

Each of the obtained samples was polished and subjected to surface X-ray diffraction measurement, and 2θ = 39. ° with respect to the (100) peak (I ₂ ) of WC near 2θ = 35.6 °.
The peak intensity ratio (I ₁ / I ₂ ) of the (101) peak (I ₁ ) of W ₂ C near 6 ° was determined. In addition, JIS1601
Flexural strength at the load of 20 kg, polishing to a mirror surface and IF
The fracture toughness (K1c) was measured by the method.

Further, the present inventors formed various surface coating layers on the surfaces of the samples in Tables 1 and 2. The film quality is described in order from the surface layer. Then, a wet cutting test was performed on each sample under the following cutting conditions, and the time until the chip was broken (cutting life) was measured.

The wet cutting test was performed while supplying an aqueous cutting oil at a rate of 5 liter / min.

(Cutting Test) Workpiece FCD 750 Tool Shape SNGN 120412 Cutting Speed 200 m / min and 400 m / min Cutting 2 mm Feed 0.3 mm / rev The results are shown in Tables 1 and 2. The chart of the X-ray diffraction measurement of the base material of Sample No. 18 in the table is shown.

[0027]

[Table 1]

[0028]

[Table 2]

From Tables 1 and 2, it can be seen that the product of the present invention having the surface coating layer has a cutting life of 2 to 6 times.
Further, it can be seen that the cutting life of the three-layer structure in which the outermost layer is coated with Al ₂ O ₃ (sample Nos. 3, 17, 21, and 23) is longer than that of a single layer or two layers. That is, the product of the present invention is 20
It can be seen that the cutting life at 0 m / min is 300 sec or more, and the cutting life at 400 m / min is 120 sec or more.

According to Tables 1 and 2, first, Sample No. 1
14 to 14, experiments were carried out under the same conditions for the amounts of Al ₂ O ₃ and the auxiliaries using raw materials having different amounts of carbon and oxygen in the WC raw materials. As a result, depending on the amount ratio of the oxygen amount and the carbon amount, W
_A change was observed in the amount of ₂ C generated, and the amount of W ₂ C tended to increase as the amount of carbon was reduced or the amount of oxygen was increased. According to the characteristic measurement results, the oxygen amount is 0.05 to 6.
Sample No. 2 having 0% by weight and a carbon content of 5.0 to 6.3% by weight
To 13 all showed high characteristics. However, in Sample No. 14 in which the amount of oxygen exceeded 6.0% by weight, the characteristics were conversely deteriorated.

Next, based on the results of Sample Nos. 1 to 14,
Using the optimal raw material of carbon amount and oxygen amount of WC raw material,
The experiment was conducted by changing the amount ratio of tungsten carbide to Al ₂ O ₃ (Sample Nos. 15 to 24). As a result, it is found that those within the scope of the present invention have excellent characteristics.

Further, based on the results from Sample Nos. 15 to 24, the amount of carbon, the amount of oxygen and the amount of Al ₂ O ₃ were kept constant,
When a similar experiment was conducted using a rare earth element oxide other than Y ₂ O ₃ as a sintering aid (samples Nos. 25 to 28), excellent characteristics were obtained as in Y ₂ O ₃ .

[0033]

As described in detail above, according to the present invention, the toughness and hardness can be improved, and the cutting life can be extended when used as a tool material by forming a surface coating layer on the surface. Accordingly, it is possible to promote application to industrial machine parts and the like that require various wear resistances such as cutting tools.

[Brief description of the drawings]

FIG. 1 is a view showing an X-ray diffraction measurement chart of a sintered body (sample No. 18) of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-177381 (JP, A) JP-A-62-56564 (JP, A) JP-A-2-131802 (JP, A) 290355 (JP, A) JP-A-5-279121 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 41/87 C04B 35/56 C04B 41/89

Claims (1)

(57) [Claims] An X-ray diffraction measurement comprising a main component comprising tungsten carbide and alumina as main components, wherein the peak height of the (101) plane of W ₂ C is I ₁ , and the peak height of the (100) plane of the WC is I ₂
, The peak intensity ratio represented by I ₁ / I ₂ is 1/1.
A surface coating layer consisting of a single layer or multiple layers is formed on the surface of the sintered body of 000 to 200/1000, and the surface coating layer is formed of a carbide, nitride,
A surface-coated tungsten carbide-alumina sintered body comprising at least one compound selected from borides, carbonitrides, carbonitrides, and oxides and oxynitrides of Al.